Update mypy CI to python 3.12

[Illviljan]

xref #9315

[Illviljan]

Strange typing errors with 3.12, the ignores fixes the following errors:

xarray/tests/test_typed_ops.py: note: In function "test_dataset_typed_ops":
xarray/tests/test_typed_ops.py:139: error: Argument 1 to "_test" has incompatible type "Variable"; expected "Dataset"  [arg-type]
xarray/tests/test_typed_ops.py:140: error: Argument 1 to "_test" has incompatible type "DataArray"; expected "Dataset"  [arg-type]
xarray/tests/test_typed_ops.py:151: error: Argument 1 to "_test" has incompatible type "Variable"; expected "Dataset"  [arg-type]
xarray/tests/test_typed_ops.py:152: error: Argument 1 to "_test" has incompatible type "DataArray"; expected "Dataset"  [arg-type]
xarray/tests/test_typed_ops.py:163: error: Argument 1 to "_test" has incompatible type "Variable"; expected "Dataset"  [arg-type]
xarray/tests/test_typed_ops.py:164: error: Argument 1 to "_test" has incompatible type "DataArray"; expected "Dataset"  [arg-type]
Found 6 errors in 1 file (checked 172 source files)

I'm not sure how to deal with this, any ideas @headtr1ck ? Are these similar issues as the other ignores in these tests?

xref #8969.

[headtr1ck]

Well, the ignores just show that the operators are not properly typed.
Maybe once 3.9 support is dropped I can try to improve this and get it working properly again...

[dcherian]

once 3.9 support is dropped

Let's do this now!

[Armavica]

Could it be linked to #9365?